How can we calculate the load of a motor ?

In a single phase motor, Use the formula P=V x A where: P=power, V=voltage; A= current. In a3-phase motor, use the formula P= V x A x sq.rt of3 x pf. Using that formula. calculating for load (amperes) or power (P)  A= P/V x1.732 x power factor. I hope it will help.

p= volt*current                                                                   in single phase motor

p=squre root 3 * volt* current* power factor                in three phase motor

You can calculate the load from the Horsepower information of the motor. One HP=746 Watts. So using the above formulas as described by Mr. Tom Escosa, you can find out Amps which determines the load.

How we can. Calculate short circuit current

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Although both of the above answers are good but if you use a Portable Energy Analyzer you can have a better of electrical quantites like PF, KVAR, KW, KVA, Amps/Phase, Volts, etc.

by using clamp ampere  to measure current for each phase